Method of granulation with a fluidized bed granulator

ABSTRACT

A granulator, having a granulation unit having a bottom floor with a perforated plate as its bottom part; an upper air-supplying pipe for supplying a fluidizing air to the bottom floor of the granulation unit; a lower air-supplying pipe; air-spouting pipes, each of which is branched from the lower air-supplying pipe, and has an opening in the bottom floor of the perforated plate, for jetting the air into the granulation unit; and spray nozzles for spraying a granulation raw material liquid, which each are provided in the center of an air outlet of the air-spouting pipe, or a granulator, having: the bottom floor; the air-supplying pipe; and spray nozzles for spraying a granulation raw material liquid each of which are provided in an opening in the bottom floor of the perforated plate, and use a high-pressure atomizing air as an auxiliary gas, wherein, in each granulator, the spray nozzles are provided in a triangular arrangement.

FIELD OF THE INVENTION

The present invention relates to an improved energy-saving granulatorand a granulation method using the same, for forming granules from amolten raw material, such as urea, sulfur, or from a slurry, forexample, of urea/ammonium sulfate containing solid state ammoniumsulfate in molten urea. In particular, the present invention relates toa granulator with a combination of a fluidized bed and a spouted bed,and to a method of granulation using the same.

BACKGROUND OF THE INVENTION

For granulators and methods of granulation for, for example, urea andurea/ammonium sulfate, in particular, many systems with a combination ofa fluidized bed and a spouted bed (hereinafter, which may be referred toas “fluidized bed/spouted bed-type granulator”) have been proposed (see,e.g. JP-B-4-63729 (“JP-B” means examined Japanese patent publication)(Claims (Claim 1), FIGS. 1 to 2), JP-A-10-216499 (“JP-A” meansunexamined published Japanese patent application) (Claims (Claims 1 to3), FIGS. 1 to 3), JP-A-11-137988 (Claims (Claims 1 to 19), FIGS. 1 to18), JP-A-54-16427 (Claims (Claims 1 to 11), FIG. 1), JP-B-60-13735(Claims (Claims 1 to 2), FIG. 1), and JP-A-60-97037 (Claims (Claims 1 to3), FIGS. 1 to 3)), which are preferably practiced currently.

FIG. 1 shows schematically a typical example of such a fluidizedbed/spouted bed-type granulator, and the technological characteristicsthereof will be described with reference to this figure.

In the figure, for example, seed particles of urea are fed as nuclei toa granulator 1, through a line 41 from a line 40, which is a feed portof the line. In the granulator 1, an aqueous urea solution containing90% by mass or more, preferably 95% by mass or more, of urea is sprayedas liquid droplets, having a diameter of 150 to 600 μm, to the nuclei ata prescribed spray angle chosen from 30 to 80 degrees, from spraynozzles 6, 7, and 8. Further, an aqueous urea solution (or molten urea)17, having a concentration of 90% by mass or more, preferably 95% bymass or more, which is fed from a urea synthesis plant or the like (notshown), is set to a temperature of 125 to 145° C., fed from a line 31 toa mixing tank (concentrator) 21, and then fed through a line 36, a pump22, and a line 37, to the spray nozzles 6, 7, and 8.

Seed particles of urea that are fed through the line 41 grow in itsgranule size while being subjected to spraying of the aqueous ureasolution in the granulator 1. In this growing of the urea granules, by aspouting air flow supplied from the lower inlet of a line 24 through alower air-supplying pipe 2 and then through air-supplying pipes 3, 4 and5 branched from the pipe 2, a spouted bed 44 is formed over each of theopenings of the air-supplying pipes, and the grown urea granulesfloating into the space 60 over the spouted beds fall, as the grownproduct (grown urea granules) 70, to the lower space 11 from the state10 floating into the upper space. On the other hand, fluidizing air issupplied from the upper inlet of a line 23, jet through a plurality ofopenings in a bottom floor 9 to the upper space, the bottom floor 9having the plurality of openings, thereby to form a fluidized bed 12 inwhich the grown granular urea 70 on the bottom floor 9 is in thefluidized state in the space 11 up to the level 12, and the growinggranular urea is fluidized as they occupy the whole space 11 over thespray nozzles 6, 7 and 8.

The bottom floor is generally rectangular in shape, and urea (nuclei)fed to one end of the bottom floor moves continuously in such movementin the fluidized bed over the bottom floor toward the other end of thebottom floor. Thus, the urea (nuclei) moves as it is graduallygranulated or enlarged, i.e. grown in granular size (diameter), andfinally the granular urea after the completion of granulation isdischarged out from an outlet of a line 25.

The proportion of those of a nominal product size among the granularurea discharged from the line 25 of the granulator 1 (hereinbelow, thisproportion is referred to as a content of the nominal product size atthe granulator outlet.), is generally 75 to 80%, and the granular ureais screened (sifted) through a screen (sieve) 13, to be separated into astandard (on-specification) product and a nonstandard(off-specification) product, with respect to the desired content of thenominal product size in a product. The standard product is passedthrough a line 26, to be stored as a product 14. On the other hand, tokeep the numbers of nuclei in the granulator 1 constant, in view of thestable continuation of the production of the product, the product havinga particle diameter greater than the specified particle diameter, andpart of the standard product, are passed through a line 27 into acrusher 15, in which they are crushed; the product having a particlediameter smaller than the specified particle diameter is passed througha line 28 and is added to those in a line 29; and the resultant mixtureis passed through a line 30 and the line 41 to the inlet of thegranulator 1, to be recycled as nuclei for the granulation.

SUMMARY OF THE INVENTION

However, although the conventional fluidized bed/spouted bed-typegranulators are considered to be technically established, the inventorsof the present invention, after studying keenly, have found that thereis still some more problems or technological difficulties to beovercome, including the followings:

(i) The minimum distance between spray nozzles configured (i.e. theminimum nozzle pitch) is determined, for prevention of interferencebetween spray nozzles for spraying the raw material liquid. Thus, thetotal area of the bottom floor (perforated plate) should be raised, andthe facility (area or volume) is getting bigger. Further, the air to beused is supplied, for example, for fluidizing of granules, drying of thesprayed raw material liquid, and cooling the product, but when thefacility is made into a bigger size, it necessitates the supply of theair in an increased amount, in particular from the viewpoint of heatbalance, resulting in a blower, a duct, and the like also made bigger;

(ii) The fluidized bed is formed over the perforated plate that is thebottom floor. The nuclei are fed to one end of the fluidized bed, andthe granulated urea is discharged out from the other end as granules.Since the bottom floor (i.e. the fluidized bed) is rectangular in shape,the operational conditions are apt to depend on the state of the inletof the fluidized bed. In particular, when the facility is made larger insize, the flow rate (throughput), temperature, and particle sizedistribution at the inlet of the fluidized bed (at the position wherethe nuclei are fed) are apt to be kept to the outlet, and it isdifficult to make those uniform in the width direction (transversedirection), i.e. in the direction perpendicular to the flow direction;and

(iii) When the linear velocity of the air for fluidization isinsufficient, it may result in a deterioration in the stability of thefluidized bed and spouted bed, to cause aggregation of granules,consequently causing an irregularly shaped product. Further, when thefluidization linear velocity is low, it causes an increase in theparticle density in the fluidized bed, to lead a problem of an increasein the pressure loss. On the other hand, a simple increase in the linearvelocity for fluidization of the air only leads to an increase in theair amount and thus an increase in the energy consumption by blowers andothers.

Accordingly, an object of the present invention is to overcome suchproblems associated with conventional fluidized bed/spouted bed-typegranulators.

According to the present invention, there is provided the followinggranulators:

(1) A granulator, comprising:

a granulation unit having a bottom floor with a perforated plate as itsbottom part;

an upper air-supplying pipe for supplying a fluidizing air to the bottomfloor of the granulation unit;

a lower air-supplying pipe; air-supplying pipes, each of which isbranched from the lower air-supplying pipe, and has an opening in thebottom floor of the perforated plate, for jetting the air into thegranulation unit; and

spray nozzles for spaying a granulation raw material liquid in a molten,solution or slurry state, each being provided in the center of an airoutlet of the air-supplying pipe,

wherein the spray nozzles are installed in the bottom floor in atriangular arrangement, and nuclei fed into the granulation unit aregranulated with the granulation raw material liquid sprayed from thespray nozzles.

(2) A granulator, comprising:

a granulation unit having a bottom floor with a perforated plate as itsbottom part;

an air-supplying pipe for supplying fluidizing air to the bottom floorof the granulation unit; and

spray nozzles for spraying a granulation raw material liquid in amolten, solution or slurry state, which are each provided in an openingin the bottom floor of the perforated plate, and use a high-pressure airas an auxiliary gas;

wherein the spray nozzles are installed in the bottom floor intriangular arrangement, and nuclei fed into the granulation unit aregranulated with the granulation raw material liquid sprayed from thespray nozzles.

(3) The granulator according to (1) or (2), wherein the perforated platehas inclined openings so that the flow direction of the fluidizing airpassing through said openings is inclined by an angle toward thevertical axis from a granule flow direction, when nuclei fed into thegranulation unit are granulated with the granulation raw material liquidsprayed from the spray nozzles.

(4) The granulator according to any one of (1) to (3), wherein thelinear velocity of fluidization of the fluidizing air is 2.0 to 3.5 m/s.

(5) The granulator according to any one of (1) to (4) wherein the pitchof the spray nozzles formed in the triangular arrangement is 0.2 to 0.5m.

Further, according to the present invention, there is provided thefollowing granulation method:

(6) A method of granulating granules, comprising:

spraying the granulation raw material liquid from the spray nozzles tonuclei fed into the granulation unit, by using the granulator accordingto any one of (1) to (5).

Other and further features and advantages of the invention will appearmore fully from the following description, appropriately referring tothe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustrative view showing one embodiment indicating aprocess for producing urea or the like according to the conventionaltechnique.

FIG. 2 is a schematic front view illustrating a spouting pipe system ofa granulator with a combination of a spouted bed and a fluidized bed(fluidized bed/spouted bed-type granulator).

FIG. 3 is a schematic side view illustrating the spouting pipe system ofa granulator with a combination of a spouted bed and a fluidized bed(fluidized bed/spouted bed-type granulator).

FIG. 4 is a schematic plan view illustrating the spouting pipe system ofa granulator with a combination of a spouted bed and a fluidized bed(fluidized bed/spouted bed-type granulator) having spray nozzles in arectangular arrangement.

FIG. 5 is a schematic plan view illustrating the spouting pipe system ofa granulator with a combination of a spouted bed and a fluidized bed(fluidized bed/spouted bed-type granulator) having spray nozzles inanother rectangular arrangement.

FIG. 6 is a schematic plan view illustrating the spouting pipe system ofa granulator with a combination of a spouted bed and a fluidized bed(fluidized bed/spouted bed-type granulator) having spray nozzles in atriangular arrangement.

FIG. 7 is a schematic front view illustrating a fluidized bed-typegranulator (fluidized bed/spouted bed-type granulator) in ahigh-pressure air spraying model.

FIG. 8 is a schematic side view illustrating the fluidized bed-typegranulator (fluidized bed/spouted bed-type granulator) in ahigh-pressure air spraying model.

FIG. 9 is a schematic plan view illustrating the fluidized bed-typegranulator (fluidized bed/spouted bed-type granulator) in ahigh-pressure air spraying model, having spray nozzles in a rectangulararrangement.

FIG. 10 is a partially enlarged plan view illustrating an example of adirectional perforated plate.

FIG. 11 is a cross-sectional view illustrating the example of adirectional perforated plate.

FIG. 12 is a graph showing the relationship between the fluidized-bed(fluid-bed) pressure loss and the linear velocity in fluidization of theair in a preferable embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, preferable embodiments of the present invention will bedescribed with reference to drawings.

FIGS. 2 to 6 schematically show an embodiment of the granulator to whichthe present invention is applied to the granulator in a urea-producingprocess as shown in FIG. 1, in comparison with conventional embodiments;and FIG. 2 is the front view, FIG. 3 is the side view, and FIGS. 4 to 6are the plan views. FIGS. 4 and 5 are the views illustrating the bottomfloors of conventional granulators, and FIG. 6 is a view illustratingthe bottom floor of the granulator of the present invention. Thereference numerals in FIGS. 2 to 6 are the same as those used in FIG. 1,if the parts or units are the same.

As shown in FIGS. 1 to 3, the granulator (also referred to as agranulation apparatus) is a so-called spouting-pipe type granulator, andfundamentally has: a bottom floor 9 as a bottom part (base) of aperforated plate in a granulation unit; an upper air-supplying pipe forsupplying the fluidizing air fed from a line 23 to the bottom floor 9 ofthe granulation unit; a lower air-supplying pipe connected to a line 24;air-supplying pipes 3, 4 and 5 branched from the lower air-supplyingpipe and extending into the bottom floor of the perforated plate to formopenings for jetting the air into the granulation unit; and spraynozzles 6, 7 and 8 provided in the center of the air outlets forspraying a granulation raw material liquid in the molten, solution orslurry state, and nuclei fed through a line 41 moves continuously in thedirection from the granulator inlet to the granulator outlet in thefluidized bed while fluidized vertically and granulated.

FIGS. 4 to 6 are views illustrating the bottom floor (perforated plate)of the granulator 1, and, as shown in FIG. 4, spray nozzles in airspouting pipes are arranged (configured) in a conventional rectangulararrangement (also referred to as a checker board-like arrangement or aserial arrangement). In the figures, 3, 4, 5 . . . representair-supplying pipes, 6, 7, 8 . . . represent spray nozzles for sprayingof the granulation raw material, which are installed in the center ofthe air outlets of the air-spouting pipes. As shown in FIG. 4, eightrows each having three spray nozzles (total spray nozzle number: 24) perrow are provided. The seeds of urea fed from the line 41 grow inparticle size while sprayed with the aqueous urea solution in thegranulator 1, and the granular urea obtained after granulation aredischarged finally through the outlet port into a line 25.

FIG. 5 is a view of an example of the bottom floor (perforated plate) 52when the number of rows of spray nozzles 51 and the number of spraynozzles 51 in each row are increased to scale up from those in FIG. 4,to conduct granulation in a greater amount, and the total fourteen rowseach having seven spray nozzles 51 per row are provided (total spraynozzle number: 98). Further, a baffle plate 53 is provided almost in thecrosswise direction in every 3 to 4 spray nozzle rows, for preventingdirect flow of the particles from the granulator inlet to the outlet.The number of baffle plates is determined appropriately, taking intoconsideration the growth of the particles, but the baffle plate isprovided generally in every 3 to 4 rows.

Such a rectangular spray nozzle arrangement leads to the problems asdescribed in the above (i) to (iii), specifically that the productionfacility should be larger, which in turn makes it difficult to controlthe temperature and distribution in particle size uniformly in thecrosswise direction to the flow and that an increase in linear velocityleads to an increase in air quantity and, consequently, an increase inenergy consumption by blowers and others.

As shown in FIG. 6, the perforated plate 52 in the granulator of thepresent invention has spray nozzles 51 in air-spouting pipes placed in atriangular arrangement (also called as a zigzag arrangement), instead ofthe rectangular arrangement as shown in FIG. 5.

For example, when the distance between spray nozzles 51 is set to 450mm, the perforated plate in the conventional example show in FIG. 5 hasseven rows of fourteen columns (the total spray nozzle number: 98),width (M1) 3,300 mm, and length (L1) 7,100 mm. The spray nozzle distance(pitch between/among spray nozzles) is a distance between the center ofa spray nozzle to the center of the adjacent another spray nozzle. Thespray nozzle distance of 450 mm is a common value used, as the minimumspray nozzle distance, for conventional granulators. A distance smallerthan that value may result in interference between spray nozzles.

On the other hand, in the triangular arrangement (the angle formed bytwo sides is 60°) as shown in FIG. 6, it is possible to form eight rowsof seven spray nozzles per row and seven rows of six spray nozzles perrow alternately in a plate of width (M2) 3,300 mm and length (L2) 6,680mm (the total spray nozzle number: 98). In the present invention, it ispossible in the triangular arrangement to make the row distance as smallas 390 mm, while keeping the minimum spray nozzle distance of 450 mm.That is, in the spray nozzle arrangement of such a triangulararrangement, it is possible to provide the same number of spray nozzlesin a smaller area and increase the number of rows to fifteen rows by onerow. The increase in the row number is equivalent to an increase in thenumber of tanks in the so-called a continuous stirred tank model, whichleads to an improvement in particle size distribution and in dryingefficiency upon granulation. Thus, the above configuration can solve allof the problems above (i) to (iii) effectively and also improves thequality of the granulated product. As shown in FIG. 6, a baffle plate 53is provided in every five spray nozzle rows. In a conventional machinein the size exemplified above, a baffle plate is necessary to be formedin every 3 to 4 spray nozzle rows, from the viewpoint of growth ofparticles, as shown in FIG. 5. In contrast, in the triangulararrangement according to the present invention, it is possible toexhibit the same favorable action as in the conventional one, even whenthe number of baffle plates is decreased, for example, under theinfluence by modification in row distance and linear velocity offluidization. A decrease in the number of baffle plates enables afurther reduction in size of the granulator. The number of baffle platescan be determined appropriately, taking the growth of the particles intoconsideration, and the baffle plate can be provided preferably in every4 to 5 spray nozzle rows.

The pitch of the spray nozzles in the triangular arrangement may varyaccording to the total spray nozzle number, the spray nozzle number perrow, the number of rows, and others, but the pitch of the spray nozzlesmutually closest is preferably 0.2 to 0.5 m.

The fluidizing air from the air-supplying pipe is fed out through theperforated plate of the bottom floor 9 of the granulator, therebyforming a fluidized bed over the bottom floor, and the openings areformed and provided in the perforated plate, in such a manner that thenuclei and growing urea or the like flow gradually and continuously inthe direction from the granulator inlet to the granulator outlet. Theflow direction of the air passing through the openings, which are formedin the perforated plate for the flow toward the granulator outletdirection, is preferably inclined in an inclined angle to the verticalaxis from the particle flow direction. This embodiment of the perforatedplate having openings with an inclined angle will be referred to as a“directional perforated plate”. FIG. 10 is a partially enlarged planview illustrating an example of the directional perforated plate. Thecross-sectional view thereof along the line A-A is shown in FIG. 11. Asshown in FIGS. 10 to 11, when the air jetted through openings 62 of aperforated plate 61 has an inclined angle, that is, the jetted-in airhas a linear velocity in the direction inclined to the bottom floor, thevelocity element in the vertical axis direction fluidizes the particlesupward to form a fluidized bed, while the velocity element in parallelwith the bottom floor exerts an action to transport and make theparticles migrate along the bottom floor toward the outlet. Because ofease in manufacture, the perforation angle of the openings is generallyset to an angle of 60 degrees or less inclined to the vertical axis.

Use of the triangularly arranged spray nozzles shown in FIG. 6 generallyresults in a problem that large aggregates do not pass effectivelybetween the spray nozzles by the air spouted from spouting pipe orjetted from the perforation of the bottom plate, but by use of thedirectional perforated plate as bottom-floor perforated plate asdescribed above, it is possible to direct the air flow jetted from eachopening outlet and thus migrate the large aggregates faster at anincreased linear velocity of fluidization toward the perforated plateoutlet (fluidized bed outlet).

The granulation method of the present invention can be carried out inaccordance with the production processes as shown in FIG. 1, using thegranulator of the present invention. The operation of the granulator 1in the method of the present invention can be carried out, by referringto operating conditions in the conventionally known methods, asdescribed in JP-B-4-63729, JP-A-10-216499, and JP-A-11-137988, exceptfor conducting the points as specified in the present invention. Thatis, for example, the number of air feed pipes may be set in a density of0.5 to 5 per m², or 6 to 10 per m², per the unit area of the bottomfloor. The spraying angle of the spray nozzles 6, 7, and 8 is generallyselected to be 30 to 80 degrees, and the rate of the air to be fed toeach of the air spouting pipes 3, 4, and 5 is, for example, selected tobe 250 to 10,000 Nm³/h. In that case, the flow velocity of the air to befed to the air spouting pipes 3, 4, and 5 is selected to be generally 5to 50 m/s, and the temperature of the air is generally selected to befrom ordinary temperature to 120° C. The height of the space 60 isselected to be generally 2 to 10 m from the bottom floor.

The fed amount of the raw material liquid per one spouted bed 44 isgenerally 0.2 to 1.2 t/h, the air quantity fed per one spouted bed 44 isgenerally 300 to 700 Nm³/h, and the flow velocity of the spouting flowis generally 15 to 150 m/s.

On the other hand, with respect to the fluidized bed 12, the linearvelocity of the air in the fluidization bed is preferably 2.0 to 3.5m/s, and the height of the level 12 (fluidized bed) is, generally, setto 0.1 to 1.0 m in the static state and 0.3 to 1.0 m in the fluidizingstate.

FIG. 12 is a graph showing the results actually measured by therelationship between the fluidized-bed (fluid-bed) pressure loss(ΔP)[mmH₂O] and the linear velocity of the air in the fluidization bed[m/s] in a preferable embodiment of the present invention at a fluidizedbed (fluid-bed) height of 600 mm and 400 mm.

In the cases of common equipment or piping, the pressure loss increasesas the flow velocity is raised, but, as shown in FIG. 12, it is apparentthat, in the fluidized bed, an increase in the linear velocity of thefluidizing air has a tendency to decrease the pressure loss. On theother hand, the higher the height of the fluidized bed, the larger thepressure loss. However, in the present invention, as shown in thefigure, even when the fluidized bed height is higher, it is possible todecrease the pressure loss by raising the linear velocity. The inventorsof the present invention found and paid attention to that point, tocomplete the present invention. That is, according to the presentinvention, by utilizing the combination of the minimization of thefluidized bed area in the triangular arrangement described above and theunique relationship between the air linear velocity and the pressureloss in the fluidized bed, it becomes possible, without increasing theair amount, to enhance the linear velocity, and to stabilize thefluidized bed with a smaller energy amount, even in a deeper fluidizedbed [i.e. at a higher height of the fluidized bed], and to form granulesof a favorable shape. Advantages of making the fluidized bed deeperinclude prevention of the droplets sprayed upward from the spray nozzlesfrom passing through the fluidized bed without participating ingranulation. When the fluidized bed is shallow, part of the dropletssprayed out of the spray nozzles pass through the fluidizing bedupwardly, without attaching to the fluidizing particles to enlarge them,followed by being solidified as the droplets are made into a dust,consequently leading to a lowered granulation efficiency.

In the present invention, the granulator may be one based on thegranulator as schematically shown in FIGS. 7 to 9. FIG. 7 is the frontview, FIG. 8 is the side view, and FIG. 9 is the plan view. In contrastto the spouting-pipe granulator shown in FIGS. 1 to 6, the granulatorshown in FIGS. 7 to 9 is a granulator called high-pressure air sprayingmodel, in which use is made, as the spray nozzles, of “spray nozzles forspraying a granulation raw material liquid, which each are provided inan opening in the bottom floor of the perforated plate, and which eachuse a high-pressure air as an auxiliary gas”. The granulator can be,however, the same as the fluidized bed/spouted bed-type granulator,except that the spraying method is different from the above one, and thebasic operation thereof can be the same as that of the granulator shownin FIGS. 1 to 6.

As shown in the figures, droplets of the raw material liquid are sprayedfrom spray nozzles 600, 700 and 800, and the gas fed from a line 240 tothe spray nozzles 600, 700 and 800 is a high-pressure air foratomization to be used as an auxiliary gas, and a spouted bed is formedover the spray nozzles by the high-pressure air in a similar manner asin the spouting pipe system. In the granulator in the embodiment shownin the figures, baffle plates 200 and 201 that block almost in thecrosswise direction a flow of the nuclei fed from the line 41 throughthe granulator inlet to the outlet, are provided at the respectiveposition higher than the level (fluidized bed) 12, although the baffleplates are basically not essential, for prevention of short pass of theparticles and the discharge thereof of insufficient size. The particlesgrow during movement through the space between the baffle plates 200 and201 and the bottom floor 9.

The spray nozzle arrangement in FIG. 9 is a conventionally knownrectangular arrangement, in which fifteen rows of six spray nozzles perrow are installed (total spray nozzle number: 90). In the presentinvention, this rectangular arrangement of spray nozzles as shown inFIG. 9 is changed to a triangular arrangement according to or similar tothat shown in FIG. 6. For example, eight rows of six spray nozzles perrow and eight rows of five spray nozzles per row (the total spray nozzlenumber 88, in the total 16 rows) may be arranged alternately, Similarlyto the spouting pipe system, use of such a triangular spray nozzlearrangement can solve all the problems (i) to (iii) above effectively,and improve the quality of the granulation product.

In the production method according to the present invention, theoperation of the granulator 1 can be carried out, by referring tooperating conditions in the conventionally known methods as described,for example, in JP-A-54-16427, JP-B-60-13735, and JP-A-60-97037, in thesimilar manner as in the spouting pipe system described above, exceptfor conducting the points as specified in the present invention.

For the operational condition for the granulator in the high-pressureair atomizing spray nozzle system, for example, as described inJP-B-60-13735, the raw-material-liquid spray nozzles 600, 700 and 800using the high-pressure atomizing air as an auxiliary gas can have aspraying angle smaller than 20 degrees, the auxiliary fluid suppliedfrom the line 240 to the vicinity of each of the spray nozzles 600, 700and 800 may be set to have a flow volume of 130 Nm³/h, the flow velocityof the auxiliary fluid may be set to 60 to 300 m/sec, the height of thelevel 12 (fluidized bed) may be set to 0.3 to 1.5 m, and the height ofthe space 60 may be et to 0.3 m to 1.5 m.

Further, similarly to the spouting pipe systems, the amount of the rawmaterial liquid to be fed per one spouted bed 44 is generally 0.2 to 1.2t/h, the air quantity to be fed per one spouted bed 44 is generally 300to 700 Nm³/h, and the flow velocity of the spouted flow is generally 15to 150 m/s.

On the other hand, with respect to the fluidized bed 12, the linearvelocity of fluidization is generally 2.0 to 3.5 m/s, and the height ofthe level 12 (fluidized bed) can be set generally to 0.1 m to 1.0 m inthe static state and 0.3 m to 1.0 m in the fluidizing state.

Hereinafter, the fluidization conditions in the granulator are describedbriefly. As shown in FIGS. 2 and 4 or FIGS. 7 and 9, when the length ofthe bottom part of the granulator in the flow direction is designated toas L, the width of the particle flow is designated to as M (L>M), andthe height is designated to as H, the internal volume V is the productof those three, and generally, the value L/M is set empirically to 2 to10.

To express the mixing properties of apparatuses, there is a multi-stagecontinuous stirred tank model that approximates the mixing properties ofthe apparatus by a series of continuous stirred tank in a number of Nwhose volumes are the same each other. It is known that, according tothe model, as the number N becomes larger, the resultant flow approachesa plug flow without any back mixing, and the distribution of theresidence time of the individual granule becomes narrower. Further, evenif the granulator is not partitioned into sections by partitioned platesbut the granulator is made into a particular spindlier shape as a whole,it is known that such a shape has an effect similar to that bypartitioning, thereby to give a narrower distribution of the residencetime of the respective granule. A particular spindlier shape is morepreferable for an increase in the number of N. In particular, inaddition to the particular spindlier shape, when the perforated plate isprovided with openings inclined so that a flow direction of the(fluidizing) air passing through said openings is inclined by an angletoward the vertical axis from a granule flow direction (which means thedirectional perforated plate), the particles move uniformly in the flowdirection, i.e. toward the granulator outlet, to give a flow that is anapproximate in the longitudinal flow with less back mixing. Thus, fromthe viewpoints in the above, by using a directional perforated plate, itis possible to make a granulator that can give a narrower residual timedistribution and exhibit the advantageous effects of the presentinvention more effectively.

As described in detail herein, by applying the triangular arrangement ofthe spray nozzles for spraying the granulation raw material liquid, thepresent invention can exhibit the following advantageous effects:

(a) It is possible to take advantage of the total area of the bottomfloor (perforated plate) more effectively. That is, since the bottomfloor area needed for installation of the same number of spray nozzlesin the triangular spray nozzle arrangement is smaller than that in thecase of the conventional rectangular spray nozzle arrangement, thegranulator can be made smaller in size. Thus, it is also possible toreduce the size of the blower, duct, and others as well;

(b) By providing the spray nozzles in the triangular arrangement, it ispossible to make the distribution of temperature and distribution ofparticle size in the direction perpendicular to the flow in thefluidized bed more uniform, especially when the granulator is madebigger in its size;

(c) As described above, by providing the spray nozzles in the triangulararrangement, the granulator can be made smaller in its size, and the airquantity does not increase excessively even when the linear velocity inthe fluidization of the air is enhanced sufficiently to assure stabilityof the fluidized bed and spouted bed, thus it is possible to assure asufficient linear velocity of fluidization, without any drastic increasein the consumption energy by blowers and others. As a result, in thefluidized bed, the particle density is lowered, and the pressure loss islowered and the probability of the particles being brought in contactwith each other is also lowered, thus it is possible to preventoccurrence of irregular shaped particles or so-called popcorn-shapedgranules, which may occur by aggregation of two or more particles; and

(d) One reason of the conventional common use of rectangular arrangedspray nozzles resides in that large aggregates, even when fed into thefluidized bed inlet, can be conveyed to pass through the space amongspray nozzles rapidly without further growth of the particles. Incontrast, if the triangular arranged spray nozzles according to thepresent invention are used, the possibility of collision of largeaggregates to the spray nozzles is increased, and this may result in thetendency to make the particles difficult to pass through the space amongthe spray nozzles. However, by using the above-mentioned directionalperforated plate of the bottom floor, to make the direction of thefluidizing air flow inclined, it is possible to raise the linearvelocity of fluidization at the respective opening outlet (moreprecisely, a component of the linear velocity of fluidization inparallel with the bottom floor), making the movement of large aggregatesmore quick to pass through rapidly the space among the spray nozzles.

The present invention is described in more detail based on the followingexamples, but the invention is not intended to be limited thereto.

EXAMPLES Reference Example 1

Urea granules were formed in a urea granulation facility of a dailyoutput of 2,000 tons, according to the same flow as shown in FIG. 1. Theurea seed particles are fed into the granulator 1 through a line 30. Theair is supplied through a duct 24 and jetted upward in the spouted bed44 at a flow velocity of 20 m/s. The upward air flow lifts the seedparticles up, to form the spouted bed. Simultaneously, separate air isfed through a line 23 to the space under the bottom floor 9, theseparate air passes through the bottom floor openings, and then risesupward in the fluidized bed at a flow velocity of 1.9 to 2.2 meter/sec.The air flow fluidizes the seed particles, to form the fluidized bed. A95% aqueous urea solution discharged from a concentrator 21 ispressurized to 1.2 MPaG by a pump 22, and sprayed upward into thespouted bed 44 in the granulator 1 at a flow rate of 1.3 tons per hourper spray nozzle (represented by the referential numbers 6, 7 and 8 inthe figure(s), but actually the number of spray nozzles is much largerin an actual urea granulation plant), allowing deposition of urea on thesurface of the seed particles fluidizing the surroundings, vaporizationof water, and solidification of the urea. The solidification heat ofurea is removed efficiently by the vaporization of water occurringsimultaneously. The seed particles grow in size gradually, duringmovement from the inlet to outlet in the granulator (from left to rightin FIG. 1), by solidification of the urea solution sprayed. The ureaparticles grown in the granulator are discharged through a line 25, intoa screen 13, where they are classified into granules of the productsize, smaller size, and larger size. Urea granules of the product sizeare discharged out as a product. The smaller sized granules are fed backinto the granulator as seed particles. The larger sized granules arecrushed in a crusher 15, and the resultant crushed urea granules arethen fed back into the granulator 1, as seed particles, together withthe smaller-sized granules. The air containing urea fine-particles(dust) discharged from the top of the granulator 1 (from a line 38) isbrought into contact with an aqueous urea solution and washed in adust-collecting unit 16, and then released into the atmosphere through aline 39. The urea dust collected is dissolved into an aqueous ureasolution, followed by feeding into a concentrator 21 through a line 35.The product 14 produced and granulated by this method was analyzed todetermine the irregular shaped urea content, which was 55 wt %. Theresults are shown in Table 1. Table 1 also shows the spouted-air flowvelocity, the fluidizing air-flow velocity, and the fluidized bed heightas well.

Reference Example 2

Urea particles were granulated in a urea granulator with a daily outputof 1,700 tons in the same flow as that in Reference Example 1, exceptthat the air flow velocity in the fluidized bed was changed to 2.4 to2.5 meters per second. The indefinite-shaped urea content in the product14 was determined to be 36 mass %, as shown in Table 1, which wasremarkably lower than that in Reference Example 1.

TABLE 1 Reference Reference Example 1 Example 2 Facility capacity t/d2,000   1,700   Spouting-pipe nozzle Rectangular Rectangular arrangementSpouted-air flow m/s 20 20 velocity Fluidizing-air flow m/s 1.9 to 2.22.4 to 2.5 velocity Fluidized bed height m   0.3   0.3 Content ofIndefinite % 55 36 shaped product

Comparative Example 1

Ninety-eight spray nozzles in a granulator with a daily output of 2,000tons were configured in a rectangular arrangement of fourteen rows ofseven spouting-pipe nozzles per row. In this case, the dimension of thebottom floor was 3.3 m×7.1 m. Table 2 shows the linear velocity in thefluidization of the air, the fluidizing air temperature, the fluidizingair flow rate, the fluidized bed height, the fluidized bed pressureloss, the granulator bottom floor area, and the fluidized bed volume.

Example 1

The spouting-pipe nozzle configuration was changed to the triangulararrangement, as a result the dimension of the bottom floor was 3.3m×6.68 m and the number of spray nozzle rows was 15. The linear velocityin the fluidization of the air and others are summarized in Table 2,similar to Comparative Example 1. As shown in Table 2, the reduction insize and increase in the number of rows were achieved at the same timein Example 1.

Example 2

The spouting-pipe nozzles in a granulator with daily output 3,300 tonswere configured in a triangular arrangement and the distance between thenozzles was made shorter, to enhance the efficiency per unit area. Thelinear velocity in the fluidization of the air and others are summarizedin Table 2, similar to Comparative Example 1. As shown in Table 2, inExample 2, the bottom floor area per ton daily output was able to bereduced by approximately 21%, compared to that in Comparative Example 1,and the linear velocity in the fluidization of the air was able to beincreased from 2.0 meters per second to 2.5 meters per second.

TABLE 2 Comparative Example 1 Example 1 Example 2 Facility capacity t/d2,000 2,000 3,300 Spouting-pipe Rectangular Triangular Triangular nozzlearrangement Number of spouting 98 98 165 pipes Number of spouting- 14 1522 pipe rows Spouted-air m/s 2.0 2.0 2.5 flow velocity (inlet standard)Fluidizing-air 44 44 44 temperature (inlet) Fluidizing-air Nm³/h 145,000143,000 220,000 flow rate Fluidized bed m 0.30 0.30 0.40 height Pressureloss mmH₂O 160 160 210 in fluidized bed Dimension of granulator m 3.3 ×7.1 3.3 × 6.68 3.5 × 8.6 bottom floor (W × L) Area of granulator m² 23.422.1 30.2 bottom floor Area of granulator m²/t/d 0.0116 0.0111 0.00915bottom floor/facility capacity Fluidized bed l/t/d 3.47 3.47 3.66 volume

INDUSTRIAL APPLICABILITY

By configuring the spray nozzles for spraying a granulation raw materialliquid in a triangular arrangement, the present invention can exhibit,for example, the following advantageous effects:

(a) Since the bottom floor area needed for installation of the samenumber of spray nozzles in the triangular spray nozzle arrangement issmaller than that in the case of the conventional rectangular spraynozzle arrangement, the granulator can be made smaller in size. Thus, itis also possible to reduce the size of the blower, duct, and others aswell;

(b) It is possible to make the distribution of temperature anddistribution of particle size in the direction perpendicular to the flowin the fluidized bed more uniform, especially when the granulator ismade bigger in its size; and further

(c) Since the air quantity does not increase excessively even when thelinear velocity in fluidization of the air is enhanced sufficiently toassure stability of the fluidized bed and spouted bed, it does not causeany drastic increase in the consumption energy by blowers and others.Thus, the present invention has an extremely broad industrialapplicability.

Having described our invention as related to the present embodiments, itis our intention that the invention not be limited by any of the detailsof the description, unless otherwise specified, but rather be construedbroadly within its spirit and scope as set out in the accompanyingclaims.

This non-provisional application claims priority under 35 U.S.C. §119(a)on Patent Application No. 2007-282040 filed in Japan on Oct. 30, 2007,which is entirely herein incorporated by reference.

1. A method of granulating granules, comprising the steps of: providinga rectangular granulation unit comprising a bottom floor with aperforated plate as its bottom part, an upper air-supplying pipe forsupplying a fluidizing air to the bottom floor of the granulation unit,a lower air-supplying pipe, air-supplying pipes branched from the lowerair-supplying pipe and having openings provided in the bottom floor ofthe perforated plate for jetting air into the granulation unit, andspray nozzles for spraying a granulation raw material liquid in a moltensolution or slurry state, with said spray nozzles being provided in thebottom floor in triangular arrangement and being provided in the centerof air outlets of the air-supplying pipes; feeding nuclei into thegranulation unit through a nuclei feed inlet; and spraying the nuclei inthe granulation unit with the granulation raw material liquid from thespray nozzles to form granules, wherein the perforated plate hasopenings inclined so that a flow direction of the fluidizing air passingthrough said openings is inclined by an angle towards the vertical axisfrom a granule flow direction towards a side of the granulation unitopposite to the nuclei feed inlet, when nuclei fed into the granulationunit are granulated with the granulation raw material liquid sprayedfrom the spray nozzles.
 2. The method according to claim 1, wherein alinear velocity of fluidization of the fluidizing air is 2.0 to 3.5 m/s.3. The method according to claim 2, wherein a pitch of the spray nozzlesformed in the triangular arrangement is 0.2 to 0.5 m.
 4. The methodaccording to claim 1, wherein a pitch of the spray nozzles formed in thetriangular arrangement is 0.2 to 0.5 m.
 5. The method according to claim1, additionally comprising the step of discharging the granules througha granule discharge outlet provided at a side opposite to the nucleifeed inlet.
 6. A method of granulating granules, comprising the stepsof: providing a rectangular granulation unit comprising a bottom floorwith a perforated plate as its bottom part, an air-supplying pipe forsupplying fluidizing air to the bottom floor of the granulation unit,and spray nozzles for spaying a granulation raw material liquid in amolten solution or slurry state which use high-pressure air and areprovided in triangular arrangement at the bottom floor of thegranulation unit; feeding nuclei into the granulation unit through anuclei feed inlet; and spraying the nuclei in the granulation unit withthe granulation raw material liquid from the spray nozzles to formgranules, wherein the perforated plate has openings inclined so that aflow direction of the fluidizing air passing through said openings isinclined by an angle towards the vertical axis from a granule flowdirection towards a side of the granulation unit opposite to the nucleifeed inlet, when nuclei fed into the granulation unit are granulatedwith the granulation raw material liquid sprayed from the spray nozzles.7. The method according to claim 6, wherein a linear velocity offluidization of the fluidizing air is 2.0 to 3.5 m/s.
 8. The methodaccording to claim 7, wherein a pitch of the spray nozzles formed in thetriangular arrangement is 0.2 to 0.5 m.
 9. The method according to claim6, wherein a pitch of the spray nozzles formed in the triangulararrangement is 0.2 to 0.5 m.
 10. The method according to claim 6,additionally comprising the step of discharging the granules through agranule discharge outlet provided at a side opposite to the nuclei feedinlet.